Micro-electromechanical (MEMS) devices having components configured to move relative to one another are widely known. An example of such a movable system is a computer storage device having a frame, mover, and a mechanical suspension interconnecting the frame and mover. Typically, the mechanical suspension holds the mover relative to the frame and allows for relative movement to occur between the mover and frame. Relative movement is achieved by applying a force to the frame and/or mover. In many cases, the applied force is provided by an actuator, such as an electrostatic drive located on the frame. The mechanical suspension typically includes flexing structures, referred to as flexures, that have spring-like characteristics. When an actuating force is applied, the mover is displaced relative to the frame from a resting or equilibrium position. When the actuating force is removed, the flexures urge the mover to return to the resting position. In data storage applications, the mover is often provided with a number of data storage locations that are accessible via operation of a read/write device located on the frame. Accessing a particular storage location may be accomplished by displacing the mover relative to the frame in a controlled manner via operation of an electrostatic drive. Effective operation of the storage device depends on the ability to precisely control and monitor the relative motion occurring between the frame and mover. In many cases, the configuration of the mechanical suspension greatly affects the ability to precisely control and monitor this relative motion.
Accordingly, it is often desirable to constrain relative motion so that the moving components are restricted from moving in a particular direction or directions. For example, the system may be configured to permit relative motion to occur only along one axis. In the data storage setting discussed above, the suspension typically permits the mover to move within a plane (e.g., the X-Y plane), but prevents it from moving in an out-of-plane direction (along the Z-axis). Constraining these devices to planar motion is often achieved by the flexures discussed above so that they flex only in certain directions. Such flexures are often described in terms of their stiffness (resistance to flexing) in a given direction. For example, a flexure system configured to allow X-Y planar motion while preventing Z-axis out-of-plane motion would be referred to as having a relatively low X-Y stiffness and a relatively high Z-axis stiffness.
Existing computer storage and other MEMS devices have various problems and limitations associated with the mechanical suspension used to interconnect the movable components. Most planar-type computer storage devices allow some amount of out-of-plane movement to occur. In terms of stiffness, such a device would be described as having a relatively high, but not infinite, Z-axis stiffness (out-of-plane stiffness). One shortcoming of many MEMS computer storage devices is that the out-of-plane stiffness varies significantly with displacement of the mover relative to the frame. Specifically, out-of-plane stiffness tends to decrease substantially in these devices the further the mover is displaced from the resting position. The wide variation in out-of-plane stiffness can significantly complicate the design of the device, since it typically is desirable to compensate for stiffness variations. Variations in in-plane stiffness is another shortcoming of many existing devices. In particular, for many MEMS devices, the in-plane stiffness of the mechanical suspension increases substantially the further the mover is displaced from the resting position. Consequently, as the mover is displaced further from the resting position, the actuator must apply a greater force to produce the same relative change in displacement. As with the previously described problem, the position-dependent behavior of the mechanical suspension can significantly complicate the design of the MEMS device and related systems.